Method of making plywood



No Drawing: I

product.- r

- .of description we will 4 of the structure Patented Oct. 18, 1932 ED"\STATES,

PATENT OFFICE THEODORE Winn mus min, or NEW WESTMINSTER, BRITISHCOLUMBIA, cANAnA,

ND IRVING r.j n ucxs AND CHARLES N. CONE, or SEATTLE, WASHINGTON,ASSIGN- ons, BY MESNE ASSIGNMENTS, TO LAMINATING PATENTS CORPORATION, orSEAIILE, WdSHINGTON, A CORPORATION OF DELAWARE I METHOD or MAKINGrLYwoon Our invention relates aim; art ofgluing and, more particularly,tolpro'cedur'es adapted for the formation of plywood and the like andinvolving the application of the adhesive in discrete-particlefor1n,"such for example, as a-dry powder or suspension of discreteparticles in a fluid; and has among its objects the controlling ofcertain of the factors which efiec't and areirelated to the gluingoperation in suchamanner, as .to' yield particularly desirable resultsand, .to provide an improved A particular featureof the invention is thecontrol of the size of the particles of the adhesive-base materialapplied. I

For purposes of clearness and definiteness set forth our inventi onasapplied to the highly exacting art of manufacturingplywood or veneering,a field characterized by presenting not only a wide range of conditionsand important factors but by these being most diflicult and complex inthe t me I By plywoodfwe 'means to include all structures embodying. atleast oneply or lamination of wood, whose thickness is not greater thancan be caused to adhere to the balance under the conditions of ourprocess. That is, of sufiicient thinness 'so that the heat of thehotpress can penetrate to the glue line sufiiciently to cause setting ofthe adhesive, and weinclude in the term plywood, alsothe term veneering.

In this connection it is to be understood that the term fwood isintended to include .not'only the natural product, but also artificialwoods having a porous structure similar feet as of plaster on lath,

. Application n; 'ipm1 m. Seria1 No. 351,822.

the penetrating elements are attached. The surfaces of Wood prepared forjoining as seen under'a microscope are very rough and perforated withnumerous openings or pores, some of which extend for a relatively greatdistance into the wood.

Whether the bond between glue and wood is formed bytrue adhesion, i. e.,specific adhesion, between the lue substance and the wood substance, orW ether the bond is mechanical, that is, due to the glue penetratinginto the numerous irregularities. of the surface of the wood and onbeing hardened in place, producing a bond due to a keying efit isobvious that other things being equal, the greater the contact the gluehas with the surface of the wood, the better will be the bond formed.

However, if the glue penetrates too deeply into the pores and otheropenings in the wood, the supply of glue between the surfaces to bejoined may be so depleted that a strong transversely continuous filmjoining the two surfaces cannot be formed, and an inferior bond willresult. This condition is known as a starved joint. When two pieces ofwood are joined with an adhesive, it will be obvious that there must bea continuous film of adhesive between the two pieces, in a transversedirection. It may be that penetration to a certain extent is necessarybeyond the boundaries of this continuous film, but the first requisiteis the transversely continuous film; this is the foundation of adhesion.

The extent to which the glue penetrates into the wood depends partly.upon the nature of the wood, which varies as to size and number ofopenings or pores. It depends also upon the eiiective pressure exertedupon the glue and also upon the fluidity or mo flucnce flow, includingalso plasticity of a discrete particle or collection ofparticles. Werecognize that in case of a suspension, if the orifice is smaller thanthe swollen particle size, then the rate of flow may depend on theplasticity of the swollen particles themselves.

In considering the penetration of an ad-.v hesive into wood underpressure the'structure of wood must be borne in mind, First inimportance are the pores of the wood, which, in general in veneer, lieina direction roughly parallel to the faces of the panel. However, many ofthe-pores are intersected by the faces so that they present openings onthe faces into which glue can readily penetrate if it is sufficientlyfluid. There are also other openings (rays) in some woods in a di--rection perpendicular to the faces. The wood cells themselves are muchsmaller but do permit penetration by the more fluid glues. Besides theseopenings natural tothe wood, .there are thechecks or cracks that areformed in the cutting of theveneer as wellv as other irregularities ofsurface- Thus with Wood there are'abundant opportunities for a fluid toescape from the surface.

For purposes of discussion,we classify the commercial methods of plywoodmanufacture with dispersed glues as follows:

A Process -'-hot press, wet veneer B Process-hot press, dry veneer CProcesscold press, dry veneer persible adhesive base in suspension inwater.

The invention contemplates the regulation of the coarseness of thepowder'inaccordan'ce with the character of theadhesive and the characterof the wood and other factors as hereinafter set forth.

The powdered adhesive may be spread on the plies of wood; If the wood-isundried containing a large part of its original sap moisture, or is wetfrom lying in water, no Water need be added. If the wood be dry, watermay be sprayed on the-adhesive layer or the tors influencingpenetration.

Penetration may take place either (a) after the press is closed andpressure is applied,

to recognize and properly control those facor. (6) before pressure isapplied. The foldered animal glue at rate of 40 lbs. per thousand.Four-panels were made as follows:

Panel 1 AGlue particles through mesh, pressure 25 lbs. per sq. in.

Panel 1 B-Glue particles on 40 mesh, pressure 25 lbs. per sq. in.

Panel 2 A Glue particles through '60 mesh, pressure 100 lbs. per sq. in;

Panel .2 BGlue'particles on 40 mesh, pressure 100 lbs. per sq. in.

All four panels were pressed with hot plates heated at 100 lbs. steampressure. The results showed the following differences:

1 A bond-"A total failure, joint completely starved and no glue appearedon the surface of the faces of the panel. No shear strength. i

, 1 B .bondPerceptible but extremely weak, joint badly starvedand noglueon faces. 37 lbs..shear strength.

2 A,bond-Fair bond,"joint much less starved, considerable glue substancepressed through the wood and appearing on the surface of the faces. 128lbs. shear strength.

2 B bond Fair, some glue appeared on the surface of the faces butmarkedly less than in 2A. 100 lbs. shear strength. i

This experiment was then'repeated with green gum veneer at 80% moistureand green birch at with plates heated with steam at 50 lbs. The resultswere as follows:

1aFailure, no bond with either wood.

,lb Failure, trace of bond with both woods spontaneously failing as thepanels cooled.

2alVeak bond, much glue substance on the face surfaces, shearstrengthsgum 54 lbs, birch 65 lbs.

2b-Fair bond, less glue substance on the face surfaces, shearstrengths-gum '98 lbs., birch 130 lbs.

Penetration may also be regulated through a control of theplasticization factor of the adhesive. i

The following indicates the effect of the use of a dispersible adhesivebase having a low plasticization factor:

A variety .of animal glue was selected and tested for viscosity with agiven amount of water. It was found to have the property of absorbing arelatively large amount of water. and produce'a solution of a givenviscosity. Another variety of animal glue (N. B, the market recognizesmany varieties of animal glue) was also similarly tested and found to beable to absorb a much lesser 1,ses,e 17

amount of water to roduce a solution of the same viscosity. e first gluewas found to have .nearl double the water requirement of the secon Thelow water sample was designated #1 and the high water #2.

Two anels were then glued up with partly dries cottonwood veneer, onepanel being spread with a definite amount of #1 glue vreduced to acoarse powder and the other with #2. The panels were then pressed in theusual way, all the conditions being maintained identical in each caseexcept for the difference in'the water requirement of theglue.substance. v

#1. panel-Weak bond Outer surface of panel. badly stained with glue, 61lbs. shear strength. V

. #2 panel-Much better bond, less stained, 110 lbs. shear strength.

This ex riment was repeated with other woods an conditions and in eachcase the glue substance, with the higher water re quirement gavemarkedly better results than a low-water requirement glue, both as toactualstrength of bond and as to visual evidence of glue penetratingcomplletely'through the plies and appearing on t e outer surface of the.anel.

T e main control, however, is exerted through the size of the particleswhich influences the penetration and affects the rate at which water isimbibed.

The size of particle has a marked effect when time is taken intoconsideration. Small particles imbibe Water faster than larger so at anygiven instant before'maximum imbibition has been reached an adhesive,un-

der the conditions given, will be more fluid if composed of smallerparticles.

In all the experiments with dispersible ma terials listed previously andsubsequently, two sets of experiments were made under each of the givenconditions, one being with small particle sizeand the other with largersize.

- VVi'thout exception the larger size particles gave the best results,whether with low or high hydraulic pressure, low or high waterrequirement glue, low or high wood moisture content, low or high heat,or with all other factors favorable.

\Ve have therefore discovered that the selection of large particles isan important means of favorably controlling results in our process whenusing highly dispersible adhesives. l/Vith more slowly dispersible ornondispersible materials particle size will of course be of less vitalimportance.

A series of experiments were tried with dispersible adhesives and greenwoods of three species representing a wide range of unfavorable typesincluding cottonwood at 125% moisture, gum at 82% and birch at 69%.Pressure, heat, particle size of glue substance and kind of gluesubstance as to moisture requirement, were controlled in favorabledirections.

Shear strength for cottonwood averaged 107 lbs.

Shear strength for gumwood averaged 122 lbs.

Shear strength for birch averaged 140 lbs.

As these results with control indicate very fair bonds in all cases,while without control no bonds are obtained, it is evident that by useof our discoveries of means of control completely dispersible adhesivesmaybe employed successfully in our process and with completely greenwoods which represents the most unfavorable condition as far as themoisture content of the wood is concerned.

It will be noted that it is the property of the adhesive of beingdispersible in water that makes it necessary to use care and to closelyregulate the other influencin factors, if good results are to beobtained. uch care,

while it is not impossible, is often beyond the limits of practicabilityin commercial operations.

It must be remembered that the condition met in gluing wet veneer withdry gluea condition the difficulty of which we purpose to solve and acondition usually obtaining in wet veneer or pliesis that there is agreat excess of water in the veneer over what is required by the glue.Under these conditions especially with green veneer the greatestadvantages are realized with the non-dispersible adhesvies, as withgreen veneer it is difficult to control the factors influencing thedegree of hydration.

Thereis found, moreover, a class of substances, or a state of matter,that is distin guished by (1) becoming plastic in contact with water,(2) drying to a strong continuous film, (3) not being dispersible by hotor cold water to any great extent. These materials are admirably adaptedbecause of these properties to be used as dry adhesives in the gluing ofgreen veneer.

Where dealing with a wood presenting coarse pores, for examplecottonwood, it is in general desirable to apply the adhesive base inparticles of a size for instance of 2035 mesh for a highly dispersibleadhesive base, and. for instance, -80 for a non-dispersible material:and where dealing with a wood of fine pore structure, for example birch,in general it is desirable to apply a dispersible adhesive base inparticles of a size for instance of 3040 and a non-dispersible base inparticles of a size for instance of 120. Again, with a wood ofmoisture-content exceeding 25 percent, it is desirable to employadhesive basc particles of 2580 percent, the coarser particles with amore dispersible adhesive; while with woods of loss moisture content itis desirable to employ particles for instance of 30120 mesh size, thedispersible adhesive being the coarser. In general also, the viscositydesirable may range for example from about 4704150 poises (as measuredby an clfiuxtype viscosimeter).

As examples of non-dispersible materials,

' reference is made to the following: soya bean flour, wheat flour (feedgrade), casein, pea flour, corn meal, oatmeal, ground rice, potatoflour, corn starch (edible) 1., linseed meal, wheat gluten, dry powderedbentonite, wheat gluten, wheat flour (feed grade) soya bean flour,casein, laundry starch 2., laundry starch 3.,crn starch (edible) 1.,corn starch (edible) 2., potato flour, rice flour, wheat gluten, wheatflour (feed grade), soya' bean flour, casein, laundry starch, cornstarch (edible), potato flour, rice flour, soya bean flour, wheatgluten, casein, soya bean flour.

Among the dispersible materials which may be utilized are animal glue orgelatin, blood albumin, soluble starch/es, and sodium silicate.

Penetration before pressure is applied can also be controlled bydecreasing the moisture content of the veneer. For example, withcompletely dispersible adhesives like animal glue we find no difiicultyin producing a strong bond on cottonwood with any moisture content inthe wood below 25% without any other method of control, but withincreasing moisture content other means of control have to be used andwith the full moisture content of 125% animal glue can be usedsuccessfully only by rigid control of all the other available factors.Cottonwood is one of the wettest of woods in its green state and it istherefore to be understood that with other woods of lower moisturecontent the problem of control of dispersible adhesives requires lessextreme methods.

With dispersible materials there is no limit to the amount of waterwhich is taken up by the adhesive, that is, if more water is present itmixes homogeneously with the adhesive layer and so the fluidity keeps onincreasing as long as more water is presented. In this case, therefore,it is more difficult to insure against excessive penetration, especiallywith wet wood. As much insurance as possible must be obtained bincreasing the particle size so that imbibition will be slower. Furtherinsurance must then be had by increasing the rate of drying to a pointso that the water of the wood will be driven quickly from it, thusdecreasing the supply of water avail able to migrate to the adhesivelayer; if both of the above regulations are not sufficient,

further control must be exercised by previously decreasing the amount ofmoisture in the wood itself so that there will not be enough present todilute. the adhesive layer to the point u'hereexcessive penetrationresults.

It will he noted that our process is also applicable to the. gluing ofdry veneer by the hot press method 8" process.

The moisture of the veneer, of course, is

:7 subject to control if our process is desired to be carried out byproviding such control; in other words, the veneer can be dried to anydegree desired before the adhesive is applied to it in the dry state.For example, it can be dried down to the point where it will supply justenough moisture to the adhesive, due regard being had to the amount ofmoisture which will escape when the heat is applied.

Also, if desired, the veneer may be dried to a very low content ofmoisture, so low in fact that it cannot supply any moisture totheadhesive substance. Under these conditions we then provide the properamount of moisture to secure the desired fluidity in the adhesive layerby adding moisture either to thesurface of the wood to be glued or tothe dry adhesive which has previously been spread on the surface of thewood, that is, the dry adhesive is first spread on the dry veneer by asuitable apparatus which gives a uniform spread and then the requiredamount of water is added to this dry adhesive by any means which willgive a uniform amount of water.

T he amount of water, of course, which is to be added must be undercontrol and may be pro-determined by trial, that is, it is found whatamount of water best suits the wood and the adhesive to secure theproper conditions of fluidity and penetration. The plies are thenassembled and pressure and heat is applied to dry the adhesive layer andset it to a permanent bond.

While in this joint application the disclosure, dealing as it does witha complex inven-.

tion, is identical in part to that of a co-pend- 10o ing application,Serial No. 335,998, filed by Theodore lVilliams Dike, as sole inventor,nevertheless in this application the claims only are made for such partof said disclosure as constitutes our joint invention.

WVe claim:

l. The method of making plywood comprising applying to the plies anadhesive base substance in the powder form dry at the time of spreadingand controlling the degree of 110 penetration of the adhesive material,an element of such control being by providing the particles of saidpowder of a predetermined size with respect to the magnitude of thepores of the plies.

2. The method of making plywood comprising applying to the plies anadhesive base substance in the powder form dry at the time of spreadingand controlling the degree of penetration of the adhesive basesubstance, an 12 element of such control being by regulating the size ofthe particles and the moisturecontent of the veneer, the size of theparticles increasing as the moisture content increases.

3. The method of making plywood com- 15 prising applying to the plies anadhesive base substance in the powder form dry at the time of spreadingand controlling the degree of penetration of the adhesive basesubstance, factors of such control being by regulating 1 the pressure,the water requirements of the adhesive base substance, the temperatureat the time of pressing, the size of the particles, the moisture contentof the veneer, and the migration of water from the veneer to the ofpenetration of the adhesive base substance" into the plies, factors ofsuch control being by regulating the fluidity of the adhesive substancethrough the amount of water which is imbibed by the adhesive base, alesser amount of water causing a.le sser penetration, said amount ofwater being governed by the size of the particles, the larger particlesize imbibing a lesser amount of water.

5. In the method of making plywood, the steps of applying to the pliesan adhesive base substance in dry discrete particle form at the time ofspreading; and controlling the degree of penetration of the adhesivebase substance into the plies, factors of such control being byregulating the fluidity of the adhesive substance through the amount ofwater which is imbibed by the adhesive base, a lesser amount of watercausing a lesser penetration, said amount of water being governed by (a)the size of the particles, the larger particle size imbibing a lesseramount of water, and (b) the moisture content of the veneer, the highermoisture content causingthe greater amount of water to be imbibed.

6. The method of gluing porous materials in the nature of wood, whichcomprises applying to a surface to be incorporated an adhesive-basesubstance in discrete-particle form, assembling and subjecting tobonding conditions, and controlling the degree or penetration of theadhesive material into the wood or the like by regulating the coarsenessof the powder.

7. The method of gluing porous materials in the nature of wood, whichcomprises applying to a surface to be incorporated an ad hesive-basesubstance in-powdered form, assembling and subjecting to bondingconditions, and controlling the degree of penetration of the adhesivematerial into the wood or the like by regulating the coarseness of thepowder.

8. The method of gluing porous materials in the nature of wood, whichcomprises applying in powdered form to a surface to be incorporated anadhesive-base substance of a character which is dispersible in water,assembling and subjecting to bonding conditions, the degree ofpenetration of the ad hesive material into the wood or the like beingcontrolled, an element in such control being the inclusion of particlesof the adhesive-base substance of a relatively large size.

9. The method of gluing porous materials in the nature of wood, whichcomprises applying in powdered form to a surface to be incorporated anadhesive-base substance of a character which is non-dispensible inwater, assembling and subjecting to bonding conditions, the degree ofpenetration of the adhesive material into the wood or the like beingcontrolled, an element in such control being limiting the maximum sizeof the particles of the base substance applied.

10. The method of gluing porous materials in the nature of wood, whichcomprises applying to a surface to be incorporated an adhesive-basesubstance in powdered form, assembling and subjecting to bondingconditions, the degree of penetration of the adhesive .material into theWood or the like being controlled, elements in such control being theregulation of the plasticization factor of the base substance utilized,the use of a base substance having a lower plasticization factor beingemployed to obtain less penetration, and the regulation of thecoarseness of the powder, a greater coarseness being utilized to obtainless penetration.

In witness whereof, we hereunto subscribe our names this 20th day ofMarch, 1929.

THEODORE WILLIAMS DIKE.

IRVING F. LAUCKS.

CHARLES N. CONE.

